The present invention relates generally to heat-transfer label assemblies and more particularly to a novel heat-transfer label assembly and to a method of using the same.
Heat-transfer labels are implements commonly used to decorate and/or to label commercial articles, such as, and without limitation to, containers for beverages (including alcoholic beverages, such as beer), essential oils, detergents, adverse chemicals, as well as health and beauty aids. As can readily be appreciated, heat-transfer labels are desirably resistant to abrasion and chemical effects in order to avoid a loss of label information and desirably possess good adhesion to the articles to which they are affixed. Heat-transfer labels are typically constructed as part of a heat-transfer label assembly, with one or more heat-transfer labels printed on a removable carrier web.
One of the earliest types of heat-transfer label assemblies is described in U.S. Pat. No. 3,616,015, inventor Kingston, which issued October, 1971, and which is incorporated herein by reference. In the aforementioned patent, there is disclosed a heat-transfer label assembly adapted for labeling plastic objects, the heat-transfer label assembly comprising a paper sheet or web, a wax release layer affixed to the paper sheet, and an ink design layer printed on the wax release layer. In the heat-transfer labeling process, the label-carrying web is subjected to heat, and the label is pressed onto a plastic article with the ink design layer making direct contact with the plastic article. As the paper sheet is subjected to heat, the wax layer begins to melt. This enables the paper sheet to be released from the ink design layer, with a portion of the wax layer being transferred with the ink design layer onto the plastic article and with a portion of the wax layer remaining with the paper sheet. After transfer of the design to the plastic article, the paper sheet is immediately removed, leaving the design firmly affixed to the plastic article and the wax transferred therewith exposed to the environment. The wax layer is thus intended to serve two purposes: (1) to provide release of the ink design from the web upon application of heat to the web and (2) to form a protective layer over the transferred ink design. After transfer of the label to the article, the transferred wax release layer is typically subjected to a post-flaming or post-heating technique which involves subjecting the transferred wax release layer to jets of high temperature gas either as direct gas flames or as hot air jets to produce wax surface temperatures of about 300° F. to 400° F. for a period of time sufficient to remelt the transferred wax. This remelting of the transferred wax is performed to enhance the optical clarity of the wax protective layer (thereby enabling the ink design layer therebeneath to be better observed) and to enhance the protective properties of the transferred wax release.
Unfortunately, despite the aforementioned post-flaming step, the transferred wax layer is often perceptible on clear and/or dark-colored objects.
Consequently, a great deal of effort has been expended in replacing or obviating the need for a wax release layer. One type of heat-transfer label assembly that does not include a wax release layer is exemplified by U.S. Pat. No. 4,935,300, inventors Parker et al., which issued Jun. 19, 1990, and which is incorporated herein by reference. In the aforementioned Parker patent, the label assembly, which is said to be particularly well-suited for use on high density polyethylene, polypropylene, polystyrene, polyvinylchloride and polyethylene terephthalate surfaces or containers, comprises a paper carrier web which is overcoated with a layer of thermoplastic polyethylene. A protective lacquer layer comprising a polyester resin and a relatively small amount of a nondrying oil is printed onto the polyethylene layer. An ink design layer comprising a resinous binder base selected from the group consisting of polyvinylchloride, acrylics, polyamides and nitrocellulose is then printed onto the protective lacquer layer. A heat-activatable adhesive layer comprising a thermoplastic polyamide adhesive is then printed onto the ink design layer.
Although the above-described Parker label assembly substantially reduces the wax-related effects discussed previously, said label assembly does not quite possess the same release characteristics of heat-transfer label assemblies containing a wax release layer. In fact, when put to commercial use, the polyethylene release layer of the Parker label assembly was found to become adhesive when subjected to the types of elevated temperatures typically encountered during label transfer. Accordingly, another type of heat-transfer label assembly differs from the Parker heat-transfer label assembly in that a very thin layer or “skim coat” of carnauba wax is interposed between the polyethylene release layer and the protective lacquer layer to improve the release of the protective lacquer from the polyethylene-coated carrier web. The thickness of the skim coat corresponds to approximately 0.1-0.4 lbs. of the wax spread onto about 3000 square feet of the polyethylene release layer. The aforementioned “skim coat-containing” heat-transfer label assembly also differs from the Parker label assembly in that the heat-activatable adhesive of the “skim coat” label assembly is printed over the entirety of the ink and protective lacquer layers, with the peripheral edges of the adhesive layer in direct contact with the wax skim coat.
An example of a “skim coat-containing” heat-transfer label assembly of the type described above is disclosed in U.S. Pat. No. 6,042,676, inventor Stein, which issued Mar. 28, 2000, and which is incorporated herein by reference. According to the aforementioned patent, a label assembly is provided that is said to be suitable for use on silane-treated glass containers, refundable polyethylene terephthalate (PET) containers, and the like. According to one embodiment, the label includes a sheet of paper overcoated with a release layer of polyethylene. A skim coat of wax is overcoated onto the polyethylene-coated paper. A protective lacquer layer comprising a polyester, polyester/vinyl or polyester/vinyl with wax lacquer is printed onto the skim coat. An ink design layer comprising one or more polyester inks is printed onto the protective lacquer layer. An adhesive layer comprising a polyester, polyester/vinyl or polyester/vinyl with wax adhesive is printed onto the ink design layer, onto any exposed portions of the protective lacquer layer and onto the skim coat in an area surrounding the protective lacquer layer.
Examples of other “skim coat-containing” heat-transfer label assemblies are disclosed in the following U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 5,800,656, inventors Geurtsen et al., issued Sep. 1, 1998; U.S. Pat. No. 6,033,763, inventors Laprade et al., issued Mar. 7, 2000; U.S. Pat. No. 6,083,620, inventors Laprade et al., issued Jul. 4, 2000; U.S. Pat. No. 6,096,408, inventors Laprade et al., issued Aug. 1, 2000; and U.S. Pat. No. 6,099,944, inventors Laprade et al., issued Aug. 8, 2000.
One feature that is common to skim coat-containing heat transfer label assemblies of the type described above is that such assemblies typically include an ink layer sandwiched between a protective lacquer layer and a heat-activatable adhesive layer. The protective lacquer layer is typically present in the assembly to provide scuff and/or chemical resistance to the label, and the adhesive layer is typically present in the assembly to promote bonding of the label to the desired article. One disadvantage, however, to the inclusion of the protective lacquer layer and/or the adhesive layer in such an assembly is that the printing of such layers to form the assembly necessarily results in a reduction in the number of available printing stations for printing the ink design layer. Consequently, the ink design layer may not possess as much detail or variation in color as may be desired. In addition, the inclusion of the protective lacquer layer and/or adhesive layer in the assembly may increase the manufacturing costs for the assembly. Consequently, it would be desirable to omit one or both of the protective lacquer and adhesive layers from a label assembly of the type described above while still retaining in the assembly the protective and adhesive properties of the omitted layers.
It should also be noted that, when using a heat-transfer label assembly of the type described above to decorate an article, one typically, prior to decoration, preheats the label assembly and pre-treats the article to be labeled. For example, where the article to be labeled is made of glass, the glass article is typically pre-treated with a silane adhesion promoter and is then typically preheated to a temperature of about 300° F. For most plastic articles, the plastic article is typically subjected, prior to decoration, to preheating using a heat-gun, a heated chamber or the like and/or is subjected to an oxidizing flame to render the article more chemically receptive to bonding. Decoration is then typically performed by applying heat to the bottom of the carrier while the top of the label is pressed against the article. Once the transferred portion of the heat-transfer label assembly has been applied to the article, the labeled article is then typically subjected to a post-treating step so that the protective lacquer layer and/or the adhesive layer, one or both of which typically comprise thermosetting resins, may be cured. (By contrast, the ink layer of the above-described heat-transfer label assembly does not typically include a thermosetting resin.) Said post-treatment step is typically performed by conveying the labeled articles through one or more industrial ovens to heat the articles to an elevated temperature, such as 400° F., for a particular amount of time, typically 15-20 minutes.
As can readily be appreciated, the above-described pre-treatment and post-treatment steps typically require the use of special equipment or materials and require time and labor to accomplish. Consequently, efforts have been undertaken to eliminate the need for such pre-treatment and/or post-treatment steps.
For example, in U.S. Pat. No. 6,344,269, inventors Makar et al., which issued Feb. 5, 2002, and which is incorporated herein by reference, there is disclosed a heat-transfer label that is said to be well-suited for use on untreated polyethylene, particularly untreated high-density polyethylene and untreated low-density polyethylene. In one embodiment, the label includes a support portion, the support portion comprising a paper carrier web overcoated with a layer of polyethylene. The label also includes a skim coat of wax overcoating the polyethylene-coated paper. The label further comprises a transfer portion printed on top of the wax skim coat, the transfer portion including a protective lacquer layer printed directly on top of at least a portion of the wax skim coat, an ink design layer printed onto a desired area of lacquer layer and a heat-activatable adhesive layer printed onto design layer, any exposed portions of lacquer layer and onto a surrounding portion of skim coat. The protective lacquer layer preferably comprises a release agent and at least one of a hard polyester resin or an acrylic resin. The ink design layer preferably comprises a polyamide ink. The adhesive layer preferably comprises a soft polyamide resin, a chlorinated polyolefin of the type that binds well to polyethylene, an ethylene vinyl acetate resin and an anti-blocking agent preferably in the form of a wax-like amide, such as erucamide.
In addition, in International Publication No. WO 03/061968, which was published Jul. 31, 2003, and which is incorporated herein by reference, there is disclosed a heat-transfer label assembly and method of using the same. The aforementioned assembly, which is said to be adapted for decorating glass articles without requiring post-treatment of the labeled glass articles, comprises, in one embodiment, a paper substrate overcoated with a layer of polyethylene, a skim coat of wax overcoated onto the polyethylene layer, and one or more heat-transfer labels printed onto the skim coat and spaced apart from one another. Each label consists of one or more ink design layers, each ink design layer comprising a binder, a colorant and a cross-linking system, the cross-linking system being adapted to effect complete cross-linking of the binder within about 1-2 minutes after the ink design layer has been transferred to a glass article that has been pre-heated to a temperature of about 250° F.-325° F. The binder comprises one or more resins selected from the group consisting of polyester resins, polyester/vinyl resins, polyamide resins, phenoxy resins, epoxy resins, polyketone resins, and acrylic resins. The binder may further include a vinyl chloride/vinyl acetate resin. The cross-linking system comprises a cross-linking resin for completely cross-linking the binder and a heat-activatable catalyst for catalyzing the cross-linking of the cross-linking resin to the binder. The cross-linker is preferably a partially methylated melamine-formaldehyde resin, and the catalyst is preferably an amine-blocked sulfonic acid catalyst.
Although the heat-transfer label assembly of the aforementioned international publication is desirable (i) in that the transferred label possesses good protective and adhesive properties, without including protective lacquer and adhesive layers, and (ii) in that post-treatment of the labeled article is unnecessary, the present inventor has found that said heat-transfer label assembly is unsuitable for use on most, if not all, flexible plastic articles, and instead, is limited in its application to glass and other inflexible articles since the label, itself, possesses very little flexibility. Consequently, if the aforementioned heat-transfer label assembly is used to label a flexible plastic article and the thus-labeled plastic article is flexed, the transferred label breaks or cracks on the flexible plastic article.
Moreover, whereas the aforementioned label assembly may be used to label glass articles without requiring post-treatment, said label assembly nonetheless still requires that the glass article be pre-treated in the conventional fashion, i.e., by silane treatment followed by pre-heating.